package sort.advanced_sort;


import java.util.Arrays;

public class Demo0_BestMergeSort {
    /**
     * 简化了辅助数组的写法
     */
    public static void mergeSort(int[] arr){
        if(arr == null || arr.length < 2){
            return;
        }
        int N = arr.length;
        sort(arr, 0, N - 1);
    }
    public static void sort(int[] arr, int lo, int hi){
        if(lo >= hi) {
            return;
        }
        int mid = lo + (hi - lo) / 2;
        sort(arr, lo, mid);
        sort(arr, mid + 1, hi);
        merge(arr, lo, mid, hi);
    }
    public static void merge(int[] arr, int lo, int mid, int hi){
        //合并后开辟辅助数组，将合并后的结果存入辅助数组中，最后在拷贝回原数组
        int[] helper = new int[hi - lo + 1];

        int left = lo, right = mid + 1;
        for(int i = 0; i < helper.length; i++){
            if(left > mid){
                helper[i] = arr[right++];
            }else if(right > hi){
                helper[i] = arr[left++];
            }else if (arr[left] <= arr[right]){
                // 等于时，先放左边可以保证归并排序的稳定性
                helper[i] = arr[left++];
            }else {
                helper[i] = arr[right++];
            }
        }
        //拷贝回原数组，注意下标的选择
        for(int i = 0; i < helper.length; i++){
            arr[lo + i] = helper[i];
        }
    }
    // for test
    public static void comparator(int[] arr) {
        Arrays.sort(arr);
    }

    // for test
    public static int[] generateRandomArray(int maxSize, int maxValue) {
        int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
        }
        return arr;
    }

    // for test
    public static int[] copyArray(int[] arr) {
        if (arr == null) {
            return null;
        }
        int[] res = new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    // for test
    public static boolean isEqual(int[] arr1, int[] arr2) {
        if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
            return false;
        }
        if (arr1 == null && arr2 == null) {
            return true;
        }
        if (arr1.length != arr2.length) {
            return false;
        }
        for (int i = 0; i < arr1.length; i++) {
            if (arr1[i] != arr2[i]) {
                return false;
            }
        }
        return true;
    }

    // for test
    public static void printArray(int[] arr) {
        if (arr == null) {
            return;
        }
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

    // for test
    public static void main(String[] args) {
        int testTime = 500000;
        int maxSize = 100;
        int maxValue = 100;
        boolean succeed = true;
        for (int i = 0; i < testTime; i++) {
            int[] arr1 = generateRandomArray(maxSize, maxValue);
            int[] arr2 = copyArray(arr1);
            mergeSort(arr1);
            comparator(arr2);
            if (!isEqual(arr1, arr2)) {
                succeed = false;
                printArray(arr1);
                printArray(arr2);
                break;
            }
        }
        System.out.println(succeed ? "Nice!" : "Fucking fucked!");

        int[] arr = generateRandomArray(maxSize, maxValue);
        printArray(arr);
        mergeSort(arr);
        printArray(arr);
    }
}
